A clarifier/thickener tank of a clarifier/thickener system serves two purposes. First, the clarifying aspect of the tank produces liquid clarified of suspended solids. Secondly, the thickener aspect of the tank concentrates the clarified suspended solids to an increased solids percentage.
Most conventional clarifier/thickener tanks have a cylindrical shape. A rectangular shape is sometimes used but is less common because of inefficiencies that can be introduced during clarification from this geometry. The cylindrical form is the most common configuration and efficient in terms of clarifier ability. The performance of the thickener aspect is independent of shape but dependent on the overall depth of the tank which provides weight from the fluid itself and the overlying thickened sludge to dewater or thicken the slurry. A clarifier/thickener tank typically has a funnel shaped bottom with steep sides to assist in removal of the solid slurry. For a conventional clarifier/thickener tank equipped with a sludge removal device such as a rake system, the slope of the bottom is about 1.5 inches for every twelve inches of run. The preferred diameter of a cylindrical clarifier/thickener tank can vary depending on the water flow rate, the density of the slurry, the slurry setting characteristics and other factors.
It is desirable to have a portable clarifier/thickener system so that the system may be transported to locations where the temporary use of the system is desired without the effort and expense of constructing and dismantling a fixed installation at each location the system is utilized. These construction and dismantling activities involve considerable expense from the labor, transportation and crane rental required to complete the installation. These costs become even more significant if the locale of operation is in a remote area or access to the site is intermittent.
The diameter of tanks which can be transported is limited by transportation laws which limit the width of a load which can be transported by road. As transported loads increase beyond a width of 10 to 12 feet, increasingly expensive and restrictive permits require purchase. For example, as load widths increase beyond 14 feet it is common for the permits to require the use of escort vehicles as well as limitations on the routes and times that the load can be transported. (See, for example, Nova Scotia Department of Transportation & Public Works, Highway Operations, Policies and Procedures Manual, Procedure Number PR5033, Mar. 5, 2006.) As a result, the transport limitations place a limit on the clarifying rate of such a system since the clarifying rate of a clarifier/thickener tank is dependent on the square foot surface area of the interior of the tank. To overcome this limitation, multiple smaller tanks can be placed in series. However, this creates complexity in the system from duplication of piping, valves, sludge pumps, feed splitters, etc. Also, the capacity to accumulate and thicken solids depends on the volume of the tank.